Balance Sheet Components (Schedule of Available-for-Sale Short-Term Investments) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Cost	$ 23,622	$ 70,479
Unrealized Gains	0	1
Unrealized Losses	(1)	(17)
Estimated Fair Value	23,621	70,463
U.S. treasuries
Debt Securities, Available-for-sale [Line Items]
Cost	23,471	70,330
Unrealized Gains	0	1
Unrealized Losses	(1)	(17)
Estimated Fair Value	23,470	70,314
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Cost	151	149
Unrealized Gains	0	0
Unrealized Losses	0	0
Estimated Fair Value	$ 151	$ 149

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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